在冻结过程中进行液体冷媒融霜的实验研究

对液体冷媒融霜系统进行了理论分析,在保温体内对-23℃的工况下进行了水的冻结试验,分别测得液体冷媒融霜和电热融霜时水的冻结速率以及在同样加湿量但不融霜时冻结水冻结过程的空白试验。试验表明:液体冷媒融霜时水的冻结速率高于电热融霜,并且液体冷媒融霜时冻结水的冻结曲线波动不大。     

The mechanism of oxide whisker growth and hot corrosion of hot-dipped Al-Si coated 430 stainless steels in air-NaCl(g) atmosphere

The mechanisms of oxide whisker growth and hot corrosion of 430 stainless steel (430SS) and aluminide 430 stainless steel hot-dipped in a Al-10 wt.%Si molten bath (430HDAS) were studied at 750 and 850 °C in air mixed with 500 and 990 vppm NaCl_(g). The results showed that the loose Cr₂O₃ scale which formed on the 430SS could not prevent the corrosion of 430SS in a 500 vppm NaCl_(g) atmosphere, resulting in the formation of Fe₂O₃ scale. Fe₂O₃ whiskers grew at the grain boundary of the Fe₂O₃ scale. However, no Fe₂O₃ whiskers formed on the Fe₂O₃ scale while 430SS was exposed in a 900 vppm NaCl_(g) atmosphere. During the initial high-temperature corrosion of 430HDAS in a 500 vppm NaCl_(g) atmosphere, a dense Al₂O₃ scale formed on the surface of the specimens. Also, Al₂O₃ whiskers grew on the Al₂O₃ scale. As exposure time increased, cyclic chlorination/oxidation degraded the protective aluminide layer and caused the formation of Fe₂O₃ scale and Fe₂O₃ whiskers. The morphology of Fe₂O₃ whiskers formed at 750 °C is more slender than those formed at 850 °C. The formation and growth of both Fe₂O₃ and Al₂O₃ whiskers may be attributed to the chloridation of both the steel substrate and aluminide layer, accelerating the diffusion rate of metallic ions in the oxide scales.     

Rotational levels of the (0 0 0) and (0 1 0) states of D2O from hot emission spectra in the 320-860 cm region

The far-infrared emission spectra of deuterated water vapour were measured at different temperatures (1370, 1520, and 1950 K) in the range 320-860 cm⁻¹ at a resolution of 0.0055 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 1150 new measured lines for the D₂¹⁶O molecule corresponding to transitions between highly excited rotational levels of the (0 0 0) and (0 1 0) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max=26 and for the (0 0 0) ← (0 0 0) band, J_max=25 and for the (0 1 0) ← (0 1 0) band, and J_max=26 and for the (0 1 0) ← (0 0 0) band. The estimated accuracy of the measured line positions is 0.0005 cm⁻¹. To our knowledge no experimentally measured rotational transitions for D₂¹⁶O within an excited vibrational state have been available in the literature so far. An extended set of experimental rotational energy levels for (0 0 0) and (0 1 0) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.0012 cm⁻¹ for 692 rotational levels of the (0 0 0) state and 0.0010 cm⁻¹ for 639 rotational levels of the (0 1 0) vibrational state. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surface [J. Chem. Phys. 106 (1997) 4618] for the (0 0 0) and (0 1 0) states is discussed.     

激光制备PMMA基PCR微流控芯片的热压键合研究

MEMS技术的发展,使得PCR微流控芯片的制备成为了现实。本文采用波长248nm的准分子激光作为一种新型的微加工方法,在19KV电压和18mm/min的激光优化加工参数下,在40mm×63mm的PMMA基片上制备出了20个循环的PCR微流控芯片。芯片上微通道的宽为104μm,深为56μm,长为1040mm,芯片加工耗时57分钟。随后采用自己搭建的热压装置,定量讨论了热压键合的温度、压力和时间对芯片键合质量的影响,得出了PMMA基微流控芯片热压键合的最佳参数:95℃,160N,20min。并在该条件下成功地将PMMA基的20个循环的PCR微流控芯片和相同尺寸的盖片键合在一起,键合后的芯片具有良好的密封性,能够承受的最大压强为0.85Mpa,能满足进行PCR反应的要求。     

Surface chemistry of hot electron and metal-oxide interfaces

Fundamental mechanisms for energy conversion and dissipation on surfaces and at interfaces have been significant issues in the community of surface science. Electronic excitation in exothermic chemical reactions or photon absorption involves the generation of energetic or hot electrons that are not in thermal equilibrium via non-adiabatic electronic excitation. A number of experimental and theoretical studies have demonstrated the influence of excited hot electrons on atomic and molecular processes, and it is a key moderator in the surface energy conversion process. The charge transfer through the metal-oxide interfaces has a significant impact on catalytic performance in mixed metal-oxide catalysts. In order to understand the influence of hot electrons and metal-oxide interfaces on the surface reactions, various detection schemes of exoelectron detection, including metal-insulator-metal and metal-semiconductor Schottky diodes, have been developed. Catalysts coupled with surface plasmons exhibit peculiar catalytic performance related to hot electron flow. In this review, we outline recent research efforts to relate hot electron flow with surface reactions occurring at metal-oxide interfaces. We report recent studies on the observation of hot electrons and the correlation between hot electrons and catalytic activity and selectivity on metallic surfaces. We show recent results from studies of surface reactions on nanocatalysts coupled with surface plasmons, where hot electron transport is the key process in energy dissipation and conversion processes.